Hi there,
Welcome to the forum!
I’ve never used Trello, but from what I Googled, Anvil would be great for this.
My suggestion would be to check out the multi-user to-do list application, and look through the tutorials to get ideas if you have not already. You may also find the secure portal, and other portal-type applications helpful for generating ideas.
In general, you could start by taking a very specific feature in Trello and try to reproduce that in Anvil, and build up from there.
Good luck!